NaCl inhibits Geotrichum citri-aurantii growth by inducing lipid droplets accumulation and enhances the biocontrol efficacy of Kloeckera apiculata 34-9

Abstract

Decays resulting from infections by Geotrichum citri-aurantii cause a significant reduction in citrus postharvest quality and marketable yield. In the present work, 0.8 mol · L-1 NaCl of Generally Recognized as Safe (GRAS) salts were identified to have complete inhibition activity to G. citri-aurantii in vitro and in vivo. An inhibitory mechanism study showed that 0.1 mol · L-1 NaCl changed the expression of six genes (Gci002087, Gci003354, Gci000013, Gci000394, Gci003505 and Gci004433) in target of rapamycin (TOR) pathway, thus inducing a large number of lipid droplets (LDs) accumulation with TEM observations and staining. In vivo, 0.1 mol · L-1 NaCl could raise up the activities of CAT, PAL, PPO and cellulase which hence to strengthen the ability of resistance tolerance of citrus. In addition, NaCl not only accelerated the growth of the biocontrol yeast Kloeckera apiculata strain 34-9, but also increased the expression level of adhesin-encoding genes and biofilm-formation encoding gene (34-9 - 3691). Finally, the storage experiments in 3 months demonstrated that the combination of NaCl and the yeast 34-9 could keep fresh, reduce decay and prolong its shelf-life, thus implying that the combination of biocontrol strain and GRAS salts has been explored as a promising alternative to synthetic fungicides.